Hazardous fluid products are transferred between a fixed storage tank and a tank on a roadway vehicle. Normally, a flexible transfer hose assembly is detachably coupled to the tank at the loading or unloading site. The opposed ends of the transfer hose assembly are normally fitted with rotatable couplings that are threaded onto male pipe ends extending from the tanks for connection of the flexible hose assembly. It is possible under certain conditions during transfer of the hazardous fluid product that the flexible hose of the hose assembly may separate from the couplings, or the flexible hose may fail, resulting in release of the hazardous product to atmosphere. Such a release of the hazardous product, such as propane or anhydrous ammonia, for example, could result in a life threatening situation.
While back check valves adjacent the tanks may, in many instances, stop the flow of the hazardous product upon failure of the flexible hose or couplings, pumps or other inline devices at the unloading tank in many instances will restrict the effectiveness of the excess flow valve typically installed in the outlet piping on the vehicle. It is necessary that flow of the hazardous fluid product be stopped at each of the tanks upon failure of the hose assembly in order to stop discharge of the hazardous product into the atmosphere.
It is desired that a safety system be provided for automatically shutting off the flow of product for each tank without human intervention upon a failure in the hose assembly between the tanks.